When William McDonough and other pioneers of the sustainable architecture movement first envisioned the concept of living, breathing buildings, it’s safe to say that they probably didn’t have structures teeming with actual living, breathing bacteria in mind. But don’t tell that to Henk Jonkers of Delft University of Technology in the Netherlands. What he and his colleagues have developed—a self-fixing bacteria-concrete hybrid—may do more to propel sustainable architecture into the mainstream than McDonough could have ever hoped for.

While it may sound unheard of, scientists have been pressing bacteria into service in construction for years. The use of mineral-producing bacteria has already been explored in a variety of applications, including the hardening of sand and in repairing cracks in concrete. But there are two problems inherent to this approach. First, the reaction that these bacteria undergo to synthesize calcium carbonate results in the production of ammonium, which is toxic at even moderate concentrations. The other problem is a more prosaic one. Since the bacteria have to be applied manually, a worker or team of workers would have to go out every few weeks to patch up every little crack on every slab of concrete—nearly defeating the purpose of making the repair process simpler and more cost-effective.

Jonkers’ solution was to track down a different bacterial strain that could live happily buried in the concrete for prolonged periods of time. Because the bacteria would be mixed into the concrete from the start, they could immediately nip small cracks in the bud before they had a chance to expand and become exposed to water, rendering them vulnerable to further wear and tear. (Concrete structures are typically reinforced with steel bars, but these can easily become corroded when water seeps into the cracks.) Such a strain would have to endure the high pH environment of concrete and churn out copious amounts of calcium carbonate without also producing large quantities of ammonium.The researchers found just the right candidates: a hardy bunch of spore-forming bacteria belonging to the genus Bacillus that make a great living in the alkaline soda lakes of Russia and Egypt. Jonkers and his colleagues placed the spores and their food source, calcium lactate, into small ceramic pellets to prevent them from being activated prematurely by the wet concrete mix and adversely affecting the integrity of the material. The spores remained dormant until the formation of a crack allowed water to sneak in, waking the bacteria and their appetite. As they began to chow down, gobbling up the calcium lactate and water, they also began to pump out calcite (a very stable form of calcium carbonate), which quickly went to work filling up the holes. Now that they’ve successfully tested the bacteria’s mettle, Jonkers and his co-workers plan on comparing the strength of their natural concrete to that of the real thing. While not examined in the New Scientist story, I imagine that it should be possible to genetically tweak the bacteria into building a stronger form of calcite (or an even tougher material) that would match up more favorably to its man-made counterpart.

For those of you who would prefer to keep bacteria out of your walls (not that you need to worry, since these particular strains wouldn’t survive outside), there are other alternatives. Michelle Pelletier, an engineer from the University of Rhode Island, has created a microencapsulated sodium silicate healing agent that, like the bacteria, springs into action when a crack begins to appear. The sodium silicate reacts with the calcium hydroxide embedded in the concrete to form a malleable gel that covers the holes and hardens within a week of activation. According to Pelletier, the material may also help ward off corrosion by enveloping the steel bars in a thin, protective film.

Though their approaches to solving the problem may differ, both Jonkers and Pelletier tout the climate benefits of their inventions: Cement production already accounts for roughly 7 percent of worldwide carbon dioxide emission production, so any technology or procedure that could make concrete structures more durable would be a welcome development.

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This could be huge for civil engineering if it can be broadly commercialized. Self-healing concrete? Concrete is everywhere! Bridges, buildings, foundations, roads, walls. All could get significantly longer lifespans and become safer as well.

I do see a couple of possible problems. If the concrete is under tension rather than compression, the bacteria may have no time to repair a crack before it separates and becomes unrepairable (by that mechanism).

Another is, if the bacteria are metabolically active even in the absence of cracking, that’s probably going to be a problem. I have trouble imagining that’s good for concrete’s structural integrity. On the other hand, if the bacteria can be persuaded to go dormant, reviving only in the presence of a crack (the presence of water is an obvious trigger but air would do too), that could work.

I can see how this can be used in the maintenance of school facilities. In many schools, with small maintenance budgets, it would be so beneficial to have the building “heal” itself. Some talk about cracks generated through wear. I can see how important it would be to be able to heal after any type of damage.

Another important factor is appearance. Concrete can easily be turned into different colors; can this be able to continue to generate colors? If the exterior can be set a specific color, painting maintenance would no longer be necessary.

Fascinating article, but from an engineering standpoint we should not give up on essential reinforcing structures. Even driveways require reinforcing mesh to keep from turning into, basically gravel. In the USA, the State of California has been using stainless steel reinforcing bars in all coastal bridges. If there is potential to increase bridge life from 50-100 years to 1000+ years, then reinforcing bars and/or cables should be made of Titanium or another highly corrosion resistant alloy. The future of this technology looks bright indeed. Even though it may not work for pre-tensioned structures like bridges, this could be used in concrete paving blocks, sidewalks, statues, stairs, park benches, foundations and boat ramps, and more. Good work, science!

can the quantity of calcite generated be controlled upto that required to fill up the holes only???…..if not so and pumped out in excess wont it cause problems like spalling……..
btw the idea and above suggested name “bio-concrete” both are fascinating

Quite a fascinating post and supporting comments that you have here. I would like to point out that other sites may make a different case, particularly in regards to natural health. Have you found additional information on the Internet, and could you give me some direction?

We used EM•1® ceramic powder in our concrete and diamond- blue finish of our pool. What that does is:
1/ Prevent creation of sulfides in the concrete that decay the concrete.
2/ Prevent the re-bars from rusting.
3/ The microbial impregnated ceramic powder’s electro-magnetic forces aline like the way they used to build “bunkers” out of concrete and Iron filings.
But also these microbial impregnated ceramic powder’s electro-magnetic forces emit beneficial vibrations that encourage an anti-Oxidant state (Does not putrefy things).